Keeping teachers in the classroom

Each year, nearly half a million teachers switch schools or leave the profession altogether. Eric Soule, who landed his first full-time job at a charter school in Riverside, California, in 2013, spent years as a substitute teacher in public schools.

"It really seemed like the school districts were stringing me along," Soule said. "[They said] 'Oh, at the end of the year we can hire you on.' And that happened year after year."

Ellen Moir, CEO of the New Teacher Center, says young teachers, in particular, frequently leave fast.

"Mostly they're getting placed in urban districts or rural America, in some of the toughest schools and some of the most under-served communities," Moir said. "And they are given a sink or swim method."

Many of them swim in the same direction.

"Typically the path is toward higher-wealth, whiter districts, where students can predicatably perform better," said Susan Moore Johnson a Research Professor at Harvard's Graduate School of Education.

Moore says her research shows that a school's culture plays a huge role. It also indicates that teachers will stay in schools where they have good leadership and feel supported.